It is taxes after all. The new Populus poll suggests that George Osborne’s talk of tax cuts rather than David Cameron’s speech was the motor behind the sharp Tory bounce in the polls. And this may have already started to wane on Thursday evening.

The final poll, based on a sample of 1,000, produces the same voting intentions – Labour 39 per cent, Conservatives 36 per cent and Liberal Democrats 15 per cent – as the version published yesterday based on 803 interviews (on Tuesday and Wednesday). However, there are tentative signs from the final 197 on Thursday, too small a sample to be robust, that the bounce may have peaked by then. (For more details see www.populus.co.uk).

When one splits the total between those interviewed before and after Mr Cameron’s speech, it is clear that the Tory advance to 36 per cent entirely occurred beforehand. Although Mr Cameron’s personal rating improved slightly after the speech, the Tory rating remained flat, while Labour support fell.

This suggests that the key events were beforehand, notably the tax-cut promises. Some 72 per cent of voters, including a similar number of Labour supporters, back the idea of “making wealthy people pay more in tax in order to take most people in Britain out of the inheritance tax net”.

A Populus poll for the BBC Two programme The Daily Politics, taken on Wednesday and Thursday, shows that the pledges to raise the inheritance tax threshold to £1 million and to exempt most first-time homebuyers from stamp duty is backed by 55 per cent of voters. Nearly three fifths (58 per cent) say it is a good idea for the Tories to make tax cuts central to their election campaign. Those aged between 18 and 34 are more likely (71 per cent) to welcome tax cut promises. The Times/Populus poll shows that three fifths of the public think that they themselves, and the country as a whole, pay too much in tax. This view is held most strongly by skilled manual workers and by Tory voters.

About a third of voters (32 per cent) believe that if the Government has any additional funds, all should be used to increase spending on public services. A quarter, including the same proportion of Tory voters, say that all funds should be used to reduce taxes; 44 per cent (including half of Tory voters) favour sharing additional money between higher spending and reduced taxes – which is the policy of all the main parties. Three fifths (62 per cent) support the idea of raising taxes on gas-guzzling cars and flights and using the money to fund tax cuts on income and other things.

Nevertheless, the BBC/Populus poll shows that despite the Tory bounce, only 44 per cent think there is a real chance that the Tories could win the next general election. Yet there is a warning for Mr Brown. Nearly three fifths (57 per cent, including 64 per cent of men) think that if he calls an election, “he will be putting the interests of the Labour Party ahead of the interests of the country”; 37 per cent disagree.

No wonder that the Brown team is awaiting further polling evidence this weekend to see whether the Tory bounce, and the impact of tax, is fading. How Mr Brown must wish that he had not boxed himself in.

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